This invention relates generally to inflatable restraint systems and, more particularly, to an apparatus and method for use in inflating an inflatable device such as an inflatable vehicle occupant restraint of a respective inflatable restraint system. More specifically, the invention relates to an inflator device having an inflation output adaptive to selected operating conditions and parameters and, in particular, to an adaptive output inflator having a selectable oxidant composition.
It is well known to protect a vehicle occupant using a cushion or bag, e.g., an "airbag," that is inflated or expanded with gas when the vehicle encounters sudden deceleration, such as in the event of a collision. In such systems, the airbag is normally housed within the vehicle in an uninflated and folded condition to minimize space requirements. Upon actuation of the system, the airbag begins being inflated in a matter of no more than a few milliseconds with gas produced or supplied by a device commonly referred to as "an inflator."
Many types of inflator devices have been disclosed in the art for the inflation of an airbag such as used in inflatable restraint systems. Prior art inflator devices include compressed stored gas inflators, pyrotechnic inflators and hybrid inflators. Unfortunately, each of these types of inflator devices is typically subject to certain disadvantages.
For example, stored gas inflators typically require the storage of a relatively large volume of gas at relatively high pressures. As a result of high gas storage pressures, the walls of the gas storage chambers of such inflators are typically relatively thick for increased strength. The combination of large volume and thick walls can result in a relatively heavy and bulky inflator design.
With respect to pyrotechnic inflators wherein gas is derived from a combustible gas generating material, i.e., a pyrotechnic, such gas generating materials can typically produce various undesirable combustion products, including various solid particulate materials. The removal of such solid particulate materials, such as by the incorporation of various filtering devices within or about the inflator, undesirably increases inflator design and processing complexity and can increase the costs associated therewith. In addition, the temperature of the gases emitted from such inflator devices can typically vary between about 500.degree. F. (260.degree. C.) and 1200.degree. F. (649.degree. C.), dependent upon numerous interrelated factors including, for example, the desired level of inflator performance, as well as the type and amount of gas generant material used therein. Consequently, airbags used in conjunction with these types of inflator devices are commonly constructed of or coated with materials which are resistant to such high temperatures. For example, an airbag such as constructed of nylon fabric, in order to resist burn through as a result of exposure to such high temperatures, can be prepared such that the nylon fabric airbag material is coated with neoprene or one or more neoprene coated nylon patches are placed at the locations of the airbag at which the hot gas initially impinges. As will be appreciated, such specially fabricated or prepared airbags are typically more costly to manufacture and produce.
Hybrid inflators, wherein airbag inflating gas results from a combination of stored compressed gas and combustion of a pyrotechnic gas generating material, also typically result in a gas having a relatively high particulate content.
Commonly assigned U.S. Pat. No. 5,470,104, Smith et al., issued Nov. 28, 1995; U.S. Pat. No. 5,494,312, Rink, issued Feb. 27, 1996; and U.S. Pat. No. 5,531,473, Rink et al., issued Jul. 2, 1996, disclose the development of a new type of inflator device which utilizes a fuel material in the form of a fluid, e.g., in the form of a gas, liquid, finely divided solid, or one or more combinations thereof. For example, in one such inflator device, the fluid fuel is burned to produce gas which contacts a quantity of stored pressurized gas to produce inflation gas for use in inflating the respective inflatable device.
In addition, various inflatable restraint system arrangements have been proposed wherein the inflation of an airbag is adjusted based on factors such as, for example, the speed of deceleration of the vehicle and seat belt usage by the occupant.
For example, U.S. Pat. No. 5,323,243 discloses an occupant sensing apparatus for use in an occupant restraint system. The disclosed sensing apparatus preferably monitors the passenger seat in the vehicle to detect the presence, position and weight of an object on the seat. A control algorithm is performed to control inflation of the airbag, responsive to the detected values.
U.S. Pat. No. 5,074,583 discloses an airbag system for an automobile including a seating condition sensor that detects a seating condition of a passenger with respect to seat position, reclining angle, as well as passenger size and posture. The invention seeks to operate the airbag system in accordance with the seating condition of the passenger such that the inflated bag is brought into optimal contact with the occupant.
In order to provide two or more performance levels, many adaptive inflation systems (including both pyrotechnic and stored gas-based systems) rely upon the use of two or more fuels or stored gases. These fuels and/or stored gases are often stored or contained separately and may be either of similar or dissimilar compositions. The need to contain or store multiple fuel and/or stored gases typically increases assembly complexity and cost.
Thus, there is a need and demand for inflator devices which reduce or simplify the number or types of gas generating or producing materials required therein and can thus assist in simplifying and reducing the costs and expenses associated with the manufacture and production of the inflator devices.
Still further, many of the above-identified types of prior art inflator devices require or rely on one or more combustion reactions for gas generation or production. Typically, the combustion of a fuel and an oxidant will only occur under certain appropriate conditions. It is often convenient to use the terms "limit of flammability" and "equivalence ratio" when seeking to express the ability of a combination of reactants to undergo a combustion reaction. A mixture of fuel and oxidant, with or without the presence of inert materials such as may serve as diluent, will normally only ignite and burn within a certain range of equivalence ratios. If certain parameters of the mixture are changed in sufficient magnitude, the mixture becomes nonflammable. At given operating conditions, the flammability operation parameter at which there is just insufficient fuel to form a flammable mixture is often referred to as the "lean limit" of flammability. Conversely, the flammability operation parameter at which, for given operating conditions, there is just an excess of fuel to form a flammable mixture is often referred to as the "rich limit" of flammability. Since a stoichiometric combustion reaction ratio can be defined for any fuel and oxidant mixture, the flammability limits for a mixture of fuel and oxidant can be expressed in terms of the equivalence ratio. The equivalence ratios at the flammability limits are referred to as the "critical equivalence ratios."
Typically, the flammability limits for a particular fuel and oxidant mixture are strongly dependent on the pressure and temperature of the mixture. Generally, the rich limit of flammability increases greatly with increasing pressure and temperature. On the other hand, however, the lean limit of flammability decreases relatively only sightly with increasing pressure.
Certain prior art adaptive inflation systems correspond to the combining or joining together of two "single output" inflators. The mounting of two individual inflators with a common diffuser is an example of such a prior art adaptive inflation system. In such an inflation system, the two individual inflators can be pyrotechnic inflators (such as with each inflator individually sized to provide an inflation output for a driver side airbag). Alternatively, such a prior art adaptive inflation system can include compressed gas inflation systems. For example, such an adaptive inflation system can include two fuel combustion chambers which share a common inert gas storage chamber.
Unfortunately, the output levels realized with such adaptive inflation systems are oftentimes not "independent" of each other. That is, such systems are not always able to provide a high level output performance corresponding to the performance level output which would normally be realized if each of the "single output" inflators were operated independently of each other and the respective outputs then appropriately combined to form a single output. While the interaction between output levels realized in such inflation systems is complex, it is believed that the reaction which controls the second level of operation may adversely affect the reaction which controls the first level of output.
In view thereof, adaptive inflation systems which provide, desirably consistent and uniform or discrete, independent levels of operation are desired and sought.
Further, with operation of at least certain of the above-described prior art adaptive inflation systems to provide only the first level of performance, the system components included to create the second (typically higher) level of performance will remain intact or "live," ready to operate. That is, such a partially-operated adaptive output inflation system typically remains partially-active and can pose or create undesired problems and risks. For example, in such a partially-operated adaptive output inflation system the system components included to create the second level of performance function or operate at some later and potentially unspecified point in time, creating a potential danger or risk.
Consequently, adaptive inflation systems which reduce or minimize the potential risks or dangers posed by the partial operation of the system are desired and sought.
While certain prior inflator devices avoid or minimize at least some of the above-identified shortcomings, there remains a need for an inflator device of simple design, construction, and operation and which, as compared to known inflation devices, can better vary output parameters such as the quantity, supply, and rate of supply of inflation gas, dependent on selected operating conditions such as ambient temperature, occupant presence, seat belt usage and rate of deceleration of the motor vehicle, for example.